Best free CMS?

Okay, I know that this is asked probably like 50 times a day here, but I really would like to know.

What is the best free CMS?

Our company have currently installed Drupal 5.x and its SO darn complicated to understand that our content managers are pulling their hair out. Not to mention we had to unprofessionally go with a pre-made theme because its impossible to understand.

We need a CMS to use for our multimedia and game design company so that its easier for us to update constantly changing game information.

We are looking into CMS Made Simple (for its excellent theming) but I would like opinions before we download and install another CMS.

Would Drupal 6 (test version) be worth trying? Is it easier to understand? I heard Joombla is resource intensive, but is it easier to use?

We basically need Easy Theming, Forums (or integration with MyBB) and User Groups. Please give us suggestions on the best free CMS to use. Thank you for your time!

Best free CMS?

I would strongly recommend silverstripe, it has a great UI and is easy to use, but I'm not sure if this would quite meet your needs for integration. Also, I've heard some good things about Plone. Both of these are open source and free to use and modify as you please.